Yield is affected by various factors, such as the number and size of the plant organs, plant architecture (for example, the number of branches), grains set length, number of filled grains, vigor (e.g. seedling), growth rate, root development, utilization of water, nutrients (e.g., nitrogen) and fertilizers, and stress tolerance.
Crops such as corn, rice, wheat, canola and soybean account for over half of total human caloric intake, whether through direct consumption of the seeds themselves or through consumption of meat products raised on processed seeds or forage. Seeds are also a source of sugars, proteins and oils and metabolites used in industrial processes. The ability to increase plant yield, whether through increase dry matter accumulation rate, modifying cellulose or lignin composition, increase stalk strength, enlarge meristem size, change of plant branching pattern, erectness of leaves, increase in fertilization efficiency, enhanced seed dry matter accumulation rate, modification of seed development, enhanced seed filling or by increasing the content of oil, starch or protein in the seeds would have many applications in agricultural and non-agricultural uses such as in the biotechnological production of pharmaceuticals, antibodies or vaccines.
Vegetable or seed oils are the major source of energy and nutrition in human and animal diet. They are also used for the production of industrial products, such as paints, inks and lubricants. In addition, plant oils represent renewable sources of long-chain hydrocarbons which can be used as fuel. Since the currently used fossil fuels are finite resources and are gradually being depleted, fast growing biomass crops may be used as alternative fuels or for energy feedstocks and may reduce the dependence on fossil energy supplies. However, the major bottleneck for increasing consumption of plant oils as bio-fuel is the oil price, which is still higher than fossil fuel. In addition, the production rate of plant oil is limited by the availability of agricultural land and water. Thus, increasing plant oil yields from the same growing area can effectively overcome the shortage in production space and can decrease vegetable oil prices at the same time.
Studies aiming at increasing plant oil yields focus on the identification of genes involved in oil metabolism as well as in genes capable of increasing plant and seed yields in transgenic plants. Genes known to be involved in increasing plant oil yields include those participating in fatty acid synthesis or sequestering such as desaturase [e.g., DELTA6, DELTA12 or acyl-ACP (Ssi2; Arabidopsis Information Resource (TAIR; arabidopsis (dot) org/), TAIR No. AT2G43710)], OleosinA (TAIR No. AT3G01570) or FAD3 (TAIR No. AT2G29980), and various transcription factors and activators such as Lec1 [TAIR No. AT1G21970, Lotan et al. 1998. Cell. 26; 93(7): 1195-205], Lec2 [TAIR No. AT1G28300, Santos Mendoza et al. 2005, FEBS Lett. 579(21):4666-70], Fus3 (TAIR No. AT3G26790), ABI3 [TAIR No. AT3G24650, Lara et al. 2003. J Biol Chem. 278(23): 21003-11] and Wri1 [TAIR No. AT3G54320, Cernac and Benning, 2004. Plant J. 40(4): 575-85].
Genetic engineering efforts aiming at increasing oil content in plants (e.g., in seeds) include upregulating endoplasmic reticulum (FAD3) and plastidal (FAD7) fatty acid desaturases in potato (Zabrouskov V., et al., 2002; Physiol Plant. 116:172-185); over-expressing the GmDof4 and GmDof11 transcription factors (Wang H W et al., 2007; Plant J. 52:716-29); over-expressing a yeast glycerol-3-phosphate dehydrogenase under the control of a seed-specific promoter (Vigeolas H, et al. 2007, Plant Biotechnol J. 5:431-41; U.S. Pat. Appl. No. 20060168684); using Arabidopsis FAE1 and yeast SLC1-1 genes for improvements in erucic acid and oil content in rapeseed (Katavic V, et al., 2000, Biochem Soc Trans. 28:935-7).
Various patent applications disclose genes and proteins which can increase oil content in plants. These include for example, U.S. Pat. Appl. No. 20080076179 (lipid metabolism protein); U.S. Pat. Appl. No. 20060206961 (the Ypr140w polypeptide); U.S. Pat. Appl. No. 20060174373 [triacylglycerols synthesis enhancing protein (TEP)]; U.S. Pat. Appl. Nos. 20070169219, 20070006345, 20070006346 and 20060195943 (disclose transgenic plants with improved nitrogen use efficiency which can be used for the conversion into fuel or chemical feedstocks); WO2008/122980 (polynucleotides for increasing oil content, growth rate, biomass, yield and/or vigor of a plant).
A common approach to promote plant growth has been, and continues to be, the use of natural as well as synthetic nutrients (fertilizers). Thus, fertilizers are the fuel behind the “green revolution”, directly responsible for the exceptional increase in crop yields during the last 40 years, and are considered the number one overhead expense in agriculture. For example, inorganic nitrogenous fertilizers such as ammonium nitrate, potassium nitrate, or urea, typically accounts for 40% of the costs associated with crops such as corn and wheat. Of the three macronutrients provided as main fertilizers [Nitrogen (N), Phosphate (P) and Potassium (K)], nitrogen is often the rate-limiting element in plant growth and all field crops have a fundamental dependence on inorganic nitrogenous fertilizer. Nitrogen is responsible for biosynthesis of amino and nucleic acids, prosthetic groups, plant hormones, plant chemical defenses, etc. and usually needs to be replenished every year, particularly for cereals, which comprise more than half of the cultivated areas worldwide. Thus, nitrogen is translocated to the shoot, where it is stored in the leaves and stalk during the rapid step of plant development and up until flowering. In corn for example, plants accumulate the bulk of their organic nitrogen during the period of grain germination, and until flowering. Once fertilization of the plant has occurred, grains begin to form and become the main sink of plant nitrogen. The stored nitrogen can be then redistributed from the leaves and stalk that served as storage compartments until grain formation.
Since fertilizer is rapidly depleted from most soil types, it must be supplied to growing crops two or three times during the growing season. In addition, the low nitrogen use efficiency (NUE) of the main crops (e.g., in the range of only 30-70%) negatively affects the input expenses for the farmer, due to the excess fertilizer applied. Moreover, the over and inefficient use of fertilizers are major factors responsible for environmental problems such as eutrophication of groundwater, lakes, rivers and seas, nitrate pollution in drinking water which can cause methemoglobinemia, phosphate pollution, atmospheric pollution and the like. However, in spite of the negative impact of fertilizers on the environment, and the limits on fertilizer use, which have been legislated in several countries, the use of fertilizers is expected to increase in order to support food and fiber production for rapid population growth on limited land resources. For example, it has been estimated that by 2050, more than 150 million tons of nitrogenous fertilizer will be used worldwide annually.
Increased use efficiency of nitrogen by plants should enable crops to be cultivated with lower fertilizer input, or alternatively to be cultivated on soils of poorer quality and would therefore have significant economic impact in both developed and developing agricultural systems.
Genetic improvement of fertilizer use efficiency (FUE) in plants can be generated either via traditional breeding or via genetic engineering.
Attempts to generate plants with increased FUE have been described in U.S. Pat. Appl. Publication No. 20020046419 (U.S. Pat. No. 7,262,055 to Choo, et al.); U.S. Pat. Appl. No. 20050108791 to Edgerton et al.; U.S. Pat. Appl. No. 20060179511 to Chomet et al.; Good, A, et al. 2007 (Engineering nitrogen use efficiency with alanine aminotransferase. Canadian Journal of Botany 85: 252-262); and Good A G et al. 2004 (Trends Plant Sci. 9:597-605).
Yanagisawa et al. (Proc. Natl. Acad. Sci. U.S.A. 2004 101:7833-8) describe Dof1 transgenic plants which exhibit improved growth under low-nitrogen conditions.
U.S. Pat. No. 6,084,153 to Good et al. discloses the use of a stress responsive promoter to control the expression of Alanine Amine Transferase (AlaAT) and transgenic canola plants with improved drought and nitrogen deficiency tolerance when compared to control plants.
Abiotic stress (ABS; also referred to as “environmental stress”) conditions such as salinity, drought, flood, suboptimal temperature and toxic chemical pollution, cause substantial damage to agricultural plants. Most plants have evolved strategies to protect themselves against these conditions. However, if the severity and duration of the stress conditions are too great, the effects on plant development, growth and yield of most crop plants are profound. Furthermore, most of the crop plants are highly susceptible to abiotic stress and thus necessitate optimal growth conditions for commercial crop yields. Continuous exposure to stress causes major alterations in the plant metabolism which ultimately leads to cell death and consequently yield losses.
Drought is a gradual phenomenon, which involves periods of abnormally dry weather that persists long enough to produce serious hydrologic imbalances such as crop damage, water supply shortage and increased susceptibility to various diseases. In severe cases, drought can last many years and results in devastating effects on agriculture and water supplies. Furthermore, drought is associated with increase susceptibility to various diseases.
For most crop plants, the land regions of the world are too arid. In addition, overuse of available water results in increased loss of agriculturally-usable land (desertification), and increase of salt accumulation in soils adds to the loss of available water in soils.
Salinity, high salt levels, affects one in five hectares of irrigated land. None of the top five food crops, i.e., wheat, corn, rice, potatoes, and soybean, can tolerate excessive salt. Detrimental effects of salt on plants result from both water deficit, which leads to osmotic stress (similar to drought stress), and the effect of excess sodium ions on critical biochemical processes. As with freezing and drought, high salt causes water deficit; and the presence of high salt makes it difficult for plant roots to extract water from their environment. Soil salinity is thus one of the more important variables that determine whether a plant may thrive. In many parts of the world, sizable land areas are uncultivable due to naturally high soil salinity. Thus, salination of soils that are used for agricultural production is a significant and increasing problem in regions that rely heavily on agriculture, and is worsen by over-utilization, over-fertilization and water shortage, typically caused by climatic change and the demands of increasing population. Salt tolerance is of particular importance early in a plant's lifecycle, since evaporation from the soil surface causes upward water movement, and salt accumulates in the upper soil layer where the seeds are placed. On the other hand, germination normally takes place at a salt concentration which is higher than the mean salt level in the whole soil profile.
Salt and drought stress signal transduction consist of ionic and osmotic homeostasis signaling pathways. The ionic aspect of salt stress is signaled via the SOS pathway where a calcium-responsive SOS3-SOS2 protein kinase complex controls the expression and activity of ion transporters such as SOS1. The osmotic component of salt stress involves complex plant reactions that overlap with drought and/or cold stress responses.
Suboptimal temperatures affect plant growth and development through the whole plant life cycle. Thus, low temperatures reduce germination rate and high temperatures result in leaf necrosis. In addition, mature plants that are exposed to excess of heat may experience heat shock, which may arise in various organs, including leaves and particularly fruit, when transpiration is insufficient to overcome heat stress. Heat also damages cellular structures, including organelles and cytoskeleton, and impairs membrane function. Heat shock may produce a decrease in overall protein synthesis, accompanied by expression of heat shock proteins, e.g., chaperones, which are involved in refolding proteins denatured by heat. High-temperature damage to pollen almost always occurs in conjunction with drought stress, and rarely occurs under well-watered conditions. Combined stress can alter plant metabolism in novel ways. Excessive chilling conditions, e.g., low, but above freezing, temperatures affect crops of tropical origins, such as soybean, rice, maize, and cotton. Typical chilling damage includes wilting, necrosis, chlorosis or leakage of ions from cell membranes. The underlying mechanisms of chilling sensitivity are not completely understood yet, but probably involve the level of membrane saturation and other physiological deficiencies. Excessive light conditions, which occur under clear atmospheric conditions subsequent to cold late summer/autumn nights, can lead to photoinhibition of photosynthesis (disruption of photosynthesis). In addition, chilling may lead to yield losses and lower product quality through the delayed ripening of maize.
Common aspects of drought, cold and salt stress response [Reviewed in Xiong and Zhu (2002) Plant Cell Environ. 25: 131-139] include: (a) transient changes in the cytoplasmic calcium levels early in the signaling event; (b) signal transduction via mitogen-activated and/or calcium dependent protein kinases (CDPKs) and protein phosphatases; (c) increases in abscisic acid levels in response to stress triggering a subset of responses; (d) inositol phosphates as signal molecules (at least for a subset of the stress responsive transcriptional changes; (e) activation of phospholipases which in turn generates a diverse array of second messenger molecules, some of which might regulate the activity of stress responsive kinases; (f) induction of late embryogenesis abundant (LEA) type genes including the CRT/DRE responsive COR/RD genes; (g) increased levels of antioxidants and compatible osmolytes such as proline and soluble sugars; and (h) accumulation of reactive oxygen species such as superoxide, hydrogen peroxide, and hydroxyl radicals. Abscisic acid biosynthesis is regulated by osmotic stress at multiple steps. Both ABA-dependent and -independent osmotic stress signaling first modify constitutively expressed transcription factors, leading to the expression of early response transcriptional activators, which then activate downstream stress tolerance effector genes.
Several genes which increase tolerance to cold or salt stress can also improve drought stress protection, these include for example, the transcription factor AtCBF/DREB 1, OsCDPK7 (Saijo et al. 2000, Plant J. 23: 319-327) or AVP1 (a vacuolar pyrophosphatase-proton pump, Gaxiola et al. 2001, Proc. Natl. Acad. Sci. USA 98: 11444-11449).
Studies have shown that plant adaptations to adverse environmental conditions are complex genetic traits with polygenic nature. Conventional means for crop and horticultural improvements utilize selective breeding techniques to identify plants having desirable characteristics. However, selective breeding is tedious, time consuming and has an unpredictable outcome. Furthermore, limited germplasm resources for yield improvement and incompatibility in crosses between distantly related plant species represent significant problems encountered in conventional breeding. Advances in genetic engineering have allowed mankind to modify the germplasm of plants by expression of genes-of-interest in plants. Such a technology has the capacity to generate crops or plants with improved economic, agronomic or horticultural traits.
Genetic engineering efforts, aimed at conferring abiotic stress tolerance to transgenic crops, have been described in various publications [Apse and Blumwald (Curr Opin Biotechnol. 13:146-150, 2002), Quesada et al. (Plant Physiol. 130:951-963, 2002), Holmstrim et al. (Nature 379: 683-684, 1996), Xu et al. (Plant Physiol 110: 249-257, 1996), Pilon-Smits and Ebskamp (Plant Physiol 107: 125-130, 1995) and Tarczynski et al. (Science 259: 508-510, 1993)].
Various patents and patent applications disclose genes and proteins which can be used for increasing tolerance of plants to abiotic stresses. These include for example, U.S. Pat. Nos. 5,296,462 and 5,356,816 (for increasing tolerance to cold stress); U.S. Pat. No. 6,670,528 (for increasing ABST); U.S. Pat. No. 6,720,477 (for increasing ABST); U.S. application Ser. Nos. 09/938,842 and 10/342,224 (for increasing ABST); U.S. application Ser. No. 10/231,035 (for increasing ABST); WO2004/104162 (for increasing ABST and biomass); WO2007/020638 (for increasing ABST, biomass, vigor and/or yield); WO2007/049275 (for increasing ABST, biomass, vigor and/or yield); WO2010/076756 (for increasing ABST, biomass and/or yield); WO2009/083958 (for increasing water use efficiency, fertilizer use efficiency, biotic/abiotic stress tolerance, yield and/or biomass); WO2010/020941 (for increasing nitrogen use efficiency, abiotic stress tolerance, yield and/or biomass); WO2009/141824 (for increasing plant utility); WO2010/049897 (for increasing plant yield).
Nutrient deficiencies cause adaptations of the root architecture, particularly notably for example is the root proliferation within nutrient rich patches to increase nutrient uptake. Nutrient deficiencies cause also the activation of plant metabolic pathways which maximize the absorption, assimilation and distribution processes such as by activating architectural changes. Engineering the expression of the triggered genes may cause the plant to exhibit the architectural changes and enhanced metabolism also under other conditions.
In addition, it is widely known that the plants usually respond to water deficiency by creating a deeper root system that allows access to moisture located in deeper soil layers. Triggering this effect will allow the plants to access nutrients and water located in deeper soil horizons particularly those readily dissolved in water like nitrates.
Cotton and cotton by-products provide raw materials that are used to produce a wealth of consumer-based products in addition to textiles including cotton foodstuffs, livestock feed, fertilizer and paper. The production, marketing, consumption and trade of cotton-based products generate an excess of $100 billion annually in the U.S. alone, making cotton the number one value-added crop.
Even though 90% of cotton's value as a crop resides in the fiber (lint), yield and fiber quality has declined due to general erosion in genetic diversity of cotton varieties, and an increased vulnerability of the crop to environmental conditions.
There are many varieties of cotton plant, from which cotton fibers with a range of characteristics can be obtained and used for various applications. Cotton fibers may be characterized according to a variety of properties, some of which are considered highly desirable within the textile industry for the production of increasingly high quality products and optimal exploitation of modem spinning technologies. Commercially desirable properties include length, length uniformity, fineness, maturity ratio, decreased fuzz fiber production, micronaire, bundle strength, and single fiber strength. Much effort has been put into the improvement of the characteristics of cotton fibers mainly focusing on fiber length and fiber fineness. In particular, there is a great demand for cotton fibers of specific lengths.
A cotton fiber is composed of a single cell that has differentiated from an epidermal cell of the seed coat, developing through four stages, i.e., initiation, elongation, secondary cell wall thickening and maturation stages. More specifically, the elongation of a cotton fiber commences in the epidermal cell of the ovule immediately following flowering, after which the cotton fiber rapidly elongates for approximately 21 days. Fiber elongation is then terminated, and a secondary cell wall is formed and grown through maturation to become a mature cotton fiber.
Several candidate genes which are associated with the elongation, formation, quality and yield of cotton fibers were disclosed in various patent applications such as U.S. Pat. No. 5,880,100 and U.S. patent application Ser. Nos. 08/580,545, 08/867,484 and 09/262,653 (describing genes involved in cotton fiber elongation stage); WO0245485 (improving fiber quality by modulating sucrose synthase); U.S. Pat. No. 6,472,588 and WO0117333 (increasing fiber quality by transformation with a DNA encoding sucrose phosphate synthase); WO9508914 (using a fiber-specific promoter and a coding sequence encoding cotton peroxidase); WO9626639 (using an ovary specific promoter sequence to express plant growth modifying hormones in cotton ovule tissue, for altering fiber quality characteristics such as fiber dimension and strength); U.S. Pat. Nos. 5,981,834, 5,597,718, 5,620,882, 5,521,708 and 5,495,070 (coding sequences to alter the fiber characteristics of transgenic fiber producing plants); U.S. patent applications U.S. 2002049999 and U.S. 2003074697 (expressing a gene coding for endoxyloglucan transferase, catalase or peroxidase for improving cotton fiber characteristics); WO 01/40250 (improving cotton fiber quality by modulating transcription factor gene expression); WO 96/40924 (a cotton fiber transcriptional initiation regulatory region associated which is expressed in cotton fiber); EP0834566 (a gene which controls the fiber formation mechanism in cotton plant); WO2005/121364 (improving cotton fiber quality by modulating gene expression); WO2008/075364 (improving fiber quality, yield/biomass/vigor and/or abiotic stress tolerance of plants).
WO publication No. 2004/104162 discloses methods of increasing abiotic stress tolerance and/or biomass in plants and plants generated thereby.
WO publication No. 2004/111183 discloses nucleotide sequences for regulating gene expression in plant trichomes and constructs and methods utilizing same.
WO publication No. 2004/081173 discloses novel plant derived regulatory sequences and constructs and methods of using such sequences for directing expression of exogenous polynucleotide sequences in plants.
WO publication No. 2005/121364 discloses polynucleotides and polypeptides involved in plant fiber development and methods of using same for improving fiber quality, yield and/or biomass of a fiber producing plant.
WO publication No. 2007/049275 discloses isolated polypeptides, polynucleotides encoding same, transgenic plants expressing same and methods of using same for increasing fertilizer use efficiency, plant abiotic stress tolerance and biomass.
WO publication No. 2007/020638 discloses methods of increasing abiotic stress tolerance and/or biomass in plants and plants generated thereby.
WO publication No. 2008/122980 discloses genes constructs and methods for increasing oil content, growth rate and biomass of plants.
WO publication No. 2008/075364 discloses polynucleotides involved in plant fiber development and methods of using same.
WO publication No. 2009/083958 discloses methods of increasing water use efficiency, fertilizer use efficiency, biotic/abiotic stress tolerance, yield and biomass in plant and plants generated thereby.
WO publication No. 2009/141824 discloses isolated polynucleotides and methods using same for increasing plant utility.
WO publication No. 2009/013750 discloses genes, constructs and methods of increasing abiotic stress tolerance, biomass and/or yield in plants generated thereby.
WO publication No. 2010/020941 discloses methods of increasing nitrogen use efficiency, abiotic stress tolerance, yield and biomass in plants and plants generated thereby.
WO publication No. 2010/076756 discloses isolated polynucleotides for increasing abiotic stress tolerance, yield, biomass, growth rate, vigor, oil content, fiber yield, fiber quality, and/or nitrogen use efficiency of a plant.
WO publication No. 2010/100595 publication discloses isolated polynucleotides and polypeptides, and methods of using same for increasing plant yield and/or agricultural characteristics.
WO publication No. 2010/049897 discloses isolated polynucleotides and polypeptides and methods of using same for increasing plant yield, biomass, growth rate, vigor, oil content, abiotic stress tolerance of plants and nitrogen use efficiency.
WO2010/143138 publication discloses isolated polynucleotides and polypeptides, and methods of using same for increasing nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content, abiotic stress tolerance and/or water use efficiency
WO publication No. 2011/080674 discloses isolated polynucleotides and polypeptides and methods of using same for increasing plant yield, biomass, growth rate, vigor, oil content, abiotic stress tolerance of plants and nitrogen use efficiency.
WO2011/015985 publication discloses polynucleotides and polypeptides for increasing desirable plant qualities.
WO2011/135527 publication discloses isolated polynucleotides and polypeptides for increasing plant yield and/or agricultural characteristics.
WO2012/028993 publication discloses isolated polynucleotides and polypeptides, and methods of using same for increasing nitrogen use efficiency, yield, growth rate, vigor, biomass, oil content, and/or abiotic stress tolerance.
WO2012/085862 publication discloses isolated polynucleotides and polypeptides, and methods of using same for improving plant properties.
WO2012/150598 publication discloses isolated polynucleotides and polypeptides and methods of using same for increasing plant yield, biomass, growth rate, vigor, oil content, abiotic stress tolerance of plants and nitrogen use efficiency.
WO2013/027223 publication discloses isolated polynucleotides and polypeptides, and methods of using same for increasing plant yield and/or agricultural characteristics.
WO2013/080203 publication discloses isolated polynucleotides and polypeptides, and methods of using same for increasing nitrogen use efficiency, yield, growth rate, vigor, biomass, oil content, and/or abiotic stress tolerance.
WO2013/098819 publication discloses isolated polynucleotides and polypeptides, and methods of using same for increasing yield of plants.
WO2013/128448 publication discloses isolated polynucleotides and polypeptides and methods of using same for increasing plant yield, biomass, growth rate, vigor, oil content, abiotic stress tolerance of plants and nitrogen use efficiency.
WO 2013/179211 publication discloses isolated polynucleotides and polypeptides, and methods of using same for increasing plant yield and/or agricultural characteristics.
WO2014/033714 publication discloses isolated polynucleotides, polypeptides and methods of using same for increasing abiotic stress tolerance, biomass and yield of plants.
WO2014/102773 publication discloses isolated polynucleotides and polypeptides, and methods of using same for increasing nitrogen use efficiency of plants.
WO2014/102774 publication discloses isolated polynucleotides and polypeptides, construct and plants comprising same and methods of using same for increasing nitrogen use efficiency of plants.
WO2014/188428 publication discloses isolated polynucleotides and polypeptides, and methods of using same for increasing plant yield and/or agricultural characteristics.
WO2015/029031 publication discloses isolated polynucleotides and polypeptides, and methods of using same for increasing plant yield and/or agricultural characteristics.